This invention relates to an engine starter and, more particularly, to an engine starter with a pinion shifter unit for a vehicular internal combustion engine.
FIG. 1 illustrates a conventional engine starter for starting a vehicular internal combustion engine. The starter 1 shown in FIG. 1 comprises a front bracket 2 having a hollow cylindrical portion 2a. A pinion shifter unit 4 supported by a bearing 3 fitted on the inner circumference of the cylindrical portion 2a is axially slidably supported on an output rotary shaft 5 through a pair of sleeve bearings 11.
The pinion shifter unit 4 comprises a undirectional clutch 6, a shifter member 7 having integrally formed at its rear end (the left end as viewed in FIG. 1) an integral clutch inner member 6a, and a pinion 8 mounted at the front end of the shifter member 7 projecting from an opening in the front bracket 2. The pinion 8 is mounted on the shifter member 7 by straight splines formed at the outer circumference of the shifter member 7 and is biased in the forward direction by a compression spring 9 placed over the shifter member 7 between the outer step portion formed in the member 7 and the inner step portion of the pinion 8. The pinion 8 is prevented from falling off from the shifter member 7 by a stopper 10.
Two sleeve bearings 11 disposed between the inner circumference of the shifter member 7 and the outer circumference of the output rotary shaft 5 are axially separated from each other and allow the shifter member 7 to rotate and axially slide relative to the output rotary shaft 21. An axial forward movement of the pinion shifter member 7 relative to the output rotary shaft 5 is limited by a stopper ring 12 secured on the front end of the output rotary shaft.
Further, the engine starter comprises a shift lever 13 for axially moving the pinion shifter unit 4, an armature rotary shaft 14, a planetary speed reduction gear unit 15 having a plurality of planetary gears 15a in mesh with a sun gear 14a formed in the armature rotary shaft 14 for reducing the speed of rotation of the armature rotary shaft 14, and a solenoid switch 16 for rocking the shift lever 13 coupled at one end to an engagement ring 17 attached to a clutch outer member 6b of the unidirectional clutch 6 and for connecting an electric power source to a d.c. motor of the starter.
The engine starter 1 as above described, which is generally referred to as the overhang type, has such a general arrangement that the outer circumferential sliding surface of the shifter member 7 of the pinion shifter unit 4 slidably fitted over the output rotary shaft 5 is slidably supported by the bearing 3 securely fitted within the front bracket 2 so that the pinion 8 mounted at the front end of the pinion shifter unit 4 may be moved into and out of engagement with an engine ring gear. In such an engine starter of the overhang type, an overhang dimension L or an axial dimension between the mounting surface 18 of the front bracket 2 at which the starter is attached to the engine and the front end of the pinion 8 when it is in an inactivated position is about 60 mm, and no overhang dimension greater than this is known to the applicant. With the overhang dimension L of the order of this length, there is substantially no problem of bending of the output rotary shaft 5 due to the load thereon. Therefore, both of two sleeve bearings 11 disposed between the shifter member 7 and the output rotary shaft 5 are made of a copper-based material in view of durability against a high-speed relative rotation.
However, a very wide variety of types of vehicles in recent years demands an engine in which the dimension between the engine surface on which a starter is to be mounted and the ring gear is equal to or more than 70 mm, whereby a starter of "super-long overhang type" having the above-mentioned overhang dimension L greater than 70 mm is required to be developed. However, when the starter output rotary shaft as well as the shifter member is made longer, it is difficult to manufacture a straight shaft, and the shaft bends relatively easily when a large load is exerted, thus posing problems in that the output rotary shaft is worn easily and the smooth sliding movement of the shifter member is impeded.